Field of the Invention
The present invention relates to the field of current probes. In particular, the present invention relates to a probe for sensing currents derived from resultant voltages on the low side (ground side) of a coaxial cable system.
Discussion of the Related Art
Conventional configurations in monitoring or probing the current and voltage along a coaxial cable often involves disruption of the coaxial association and/or characteristics of the inner and outer conductors. The most common way of disrupting the association is to use an AC current probe, current transformer/transducer or a resistive element somewhere along the coaxial path. However, the use of such components often impacts the impedance of the cable itself leading to deleterious effects, such as, undesirable reflections in pulsed applications. Moreover, when high voltages are conducted by the transmission line, the inserted component itself is also exposed to the high voltage making the measurement more difficult. Moreover, some inserted components often also include special fittings and adaptors which not only interfere with the purpose of the coaxial conductors, but in doing so, interject cumbersome structures which often affect the versatility of an inherent coaxial cable design.
Background information on a current monitor that includes coaxial cables, is described and claimed in, U.S. Pat. No. 7,4242,197, entitled, “CURRENT MEASURING APPARATUS, TEST APPARATUS, AND COAXIAL CABLE AND ASSEMBLED CABLE FOR THE APPARATUSES,” issued Jul. 10, 1996, to Sataou et al., including the following, “[t]here is provided a current measuring apparatus for measuring current-under-measurement flowing between a first measuring terminal and a second measuring terminal, having a plurality of primary coils whose one end is electrically connected with the first measuring terminal and another end thereof is electrically connected with the second measuring terminal, a secondary coil that generates voltage representing the current-under-measurement corresponding to the current-under-measurement flowing through the plurality of primary coils and coaxial cables, each corresponding to the plurality of primary coils and having a signal line that connects one end of the primary coil with the first measuring terminal and a shield, and the coaxial cable has the signal line, an insulating layer for coating the signal line, first one of the shield having a tape-like conductor wound around the insulating layer and second one of the shield made of a conductor provided around the first shield.”
Background information on a measuring apparatus for determining energy flow through a coaxial cable, is described and claimed in, EP Patent No. 0,792,464, entitled, “A MEASURING LINE FOR A COAXIAL CONDUCTOR FOR DETERMINING ENERGY THROUGHFLOW AND STANDING WAVE RATIOS” issued Nov. 24, 1998, to Gunnar Persson, including the following, “[a]measuring line (1) for coupling with coaxial contacts (2) comprises a 50 ohms slabline having a centre conductor (3) and on one side thereof a single directional coupler (4) of higher impedence, e.g. 75 ohms, whose ends are coupled with accurate matching, through the medium of carrier cylinders (8), to attenuating and impedence-transforming circuits (30) constructed in accordance with microstrip technique on an externally mounted circuit board (10). The attenuated signal is measured in a circuit which includes a feedback voltage-controlled attenuating circuit.”
Background information on an apparatus that utilizes a Rogowski transducer to measure current in a conductor, such as coaxial cable, is described and claimed in, EP Patent No. 1,073,908, entitled, “CURRENT MEASURING DEVICE” issued Mar. 24, 2004, to Frederick et al., including the following, “[a]current measuring device comprising a Rogowski coil (30). Connected across ends of the coil (30) is a passive integrator in two parts (34, 36), the parts being connected by a coaxial cable (32). Connected to the output of the passive integrator (34, 36), is an electronic integrator (38). At low frequencies the passive integrator (34, 36) has a substantially constant gain and the electronic integrator (38) integrates the signal from the coil (30). At high frequencies, the electronic integrator (38) has substantially constant gain and the passive integrator (34, 36) integrates the signal from the coil (30). In order to reduce high frequency voltage oscillations, the Rogowski coil (30) is terminated with a coil damping resistor that has a value that is approximately the same as a characteristic impedance of the coil.”
Background information on a coaxial probe that maps current densities of an electron beam, is described and claimed in, U.S. Pat. No. 4,629,975, entitled, “COAXIAL PROBE FOR MEASURING THE CURRENT DENSITY PROFILE OF INTENSE ELECTRON BEAMS” issued Dec. 16, 1986, to Fiorito et al., including the following, “[a]An interceptive type electric probe for mapping the radial current densityrofile of high energy and high current electron beams comprises an input sensor, an interface support connector and an output support connector. The entire structure of the electric probe is configured to closely approximate a coaxial transmission line of a predetermined impedance that is opened ended but yet shielded. The nature of the construction of the probe, in terms of materials and techniques, allows for survival thereof in high temperature and intense beam environments.”
Background information on a coaxial current probe, is described and claimed in, U.S. Pat. No. 5,066,904, entitled, “COAXIAL CURRENT SENSORS” issued Nov. 19, 1991, to Donald F. Bullock, including the following, “[a]sensor for measuring large magnitudes of A.C. current utilizes a current divider having parallel conductors and a current comparator coupled to one of the conductors so arranged as to perform first and second stages of scaling of the A.C. current to obtain an output signal from the sensor proportional to the A.C. current. The overall sensor ratio is the product of the ratios of the first and second stages, thereby permitting very large ratios to be obtained. Components of the sensor are arranged so as to cause cancellation of magnetic fields by the sensor and to make the sensor immune from incident magnetic fields.”
The present embodiments disclosed herein are directed to a novel coaxial current monitor that capitalizes on the mirror currents that are part of a coaxial cable transmission line. In particular, because of the current within the inner surface of the shield is the image of the inner conductor the coaxial cable, breaking into the shield with configured impedances in a novel manner and measuring resultant voltages across the constructed impedances enables the measurement of a derived current running through the inner conductor of the coaxial cable because of the mirror image current property. In addition, because the mirror image current is being measured via flow through the low impedance portion of the shield, the design(s) herein enable safe measurements even if high voltages are being utilized along the coaxial cable.